Subliminal stimuli (/sʌbˈlɪmɪnəl/) (the prefix sup- literally
"below, or less than", while the prefix sub- literally "up to"),[1]
contrary to supraliminal stimuli or "above threshold", are any sensory
stimuli below an individual's threshold for conscious perception.[2] A
recent review of functional magnetic resonance imaging (fMRI) studies
shows that subliminal stimuli activate specific regions of the brain
despite participants being unaware.[3] Visual stimuli may be quickly
flashed before an individual can process them, or flashed and then
masked, thereby interrupting the processing. Audio stimuli may be
played below audible volumes or masked by other stimuli.

5 Consumption and television
6 See also
7 References
8 Further reading

Effectiveness[edit]
Applications of subliminal stimuli often base themselves on the
persuasiveness of the message. Importantly, research on action priming
has shown that subliminal stimuli can trigger only actions a receiver
of the message plans to perform anyway; however, consensus of this
finding remains unsubstantiated by other research. Most actions can be
triggered subliminally only if the person already has the potential to
perform a specific action.[4] The following sections have more
information on specific studies which investigate the effectiveness of
subliminal stimuli.[5][6]
Method[edit]
The threshold in subliminal stimuli research is the level at which the
participant is not aware of the stimulus being presented.[7]
Researchers determine a threshold for the stimulus that will be used
as the subliminal stimulus. That subliminal stimulus is then presented
during the study at some point and measures are taken to determine the
effects of the stimulus. The way in which studies operationally define
thresholds depends on the methods of the particular article. The
methodology of the research also varies by the type of subliminal
stimulus (auditory or visual) and the dependent variables they
measure.
Objective threshold[edit]
The objective threshold is found using a forced choice procedure, in
which participants must choose which stimulus they saw from options
given to them.[7] Participants are flashed a stimulus (e.g. the word
"orange") and then given a few choices and asked which one they saw.
Participants must choose an answer in this design. The objective
threshold is obtained when participants are at chance level of
performance in this task.[7] The length of presentation that causes
chance performance on the forced choice task is used later in the
study for the subliminal stimuli.
Subjective threshold[edit]
The subjective threshold is determined by when the participant reports
that his or her performance on the forced choice procedure
approximates chance.[7] The subjective threshold is 30 to 50 ms slower
than the objective threshold, demonstrating that participants are able
to detect the stimuli is present sooner than their perceived accuracy
ratings would indicate.[7] In other words, stimuli presented at a
subjective threshold have a longer presentation time than those
presented at an objective threshold. When using the objective
threshold, primes neither facilitated nor inhibited the recognition of
a color.[7] However, the longer the duration of the priming stimuli,
the greater effect it had on subsequent responding.[7] These findings
indicate that the results of some studies may be due to their
definition of below threshold.
Direct and indirect measures[edit]
PerceptionPerception without awareness can be demonstrated through the
comparison of direct and indirect measures of perception.[8] Direct
measures use responses to task definitions as per the explicit
instructions given to the subjects. Indirect measures use responses
that are not a part of the task definition given to subjects.[8] Both
direct and indirect measures are displayed under comparable conditions
except for the direct or indirect instruction. For example, in a
typical Stroop Task, subjects are given the task of naming the color
of a patch of ink. A direct measure is 'accuracy'—true to the
instructions given to the participants. The popular indirect measure
used in the same task is 'response time'—subjects are not told that
they are being measured for response times.
Similarly, a direct effect is the effect of a task stimulus on the
instructed response to that stimulus, usually measured as accuracy. An
indirect effect is an uninstructed effect of the task stimulus on
behavior, sometimes measured by including an irrelevant or distracting
component in the task stimulus and measuring its effect on
accuracy.[9] These effects are then compared on their relative
sensitivity: an indirect effect that is greater than direct effect
indicates existence of unconscious cognition.[8][9]
Visual stimuli[edit]
In order to study the effects of subliminal stimuli, researchers will
often prime the participants with specific visual stimuli, often
images, and determine if those stimuli elicit different
responses.[10][11]
Subliminal stimuli have mostly been studied in the
context of emotion, in particular, researchers have focused a lot of
attention to the perception of faces and how subliminal presentation
to different facial expression affects emotion.[12][13][14][15] Visual
subliminal stimuli has also been used to study emotion eliciting
stimuli and simple geometric stimuli.[16][17][18][19] A significant
amount of research has been produced throughout the years to
demonstrate the effects of subliminal visual stimuli.[20]
Images[edit]
Attitudes can develop without being aware of its antecedents.[10]
Individuals viewed slides of people performing familiar daily
activities after being exposed to either an emotionally positive
scene, such as a romantic couple or kittens, or an emotionally
negative scene, such as a werewolf or a dead body between each slide
and the next. After exposure from something which the individuals
consciously perceived as a flash of light, the participants gave more
positive personality traits to those people whose slides were
associated with an emotionally positive scene and vice versa. Despite
the statistical difference, the subliminal messages [21] had less of
an impact on judgment than the slide's inherent level of physical
attractiveness.[10]
Individuals show right amygdala activity in response to subliminal
fear, and greater left amygdala response to supraliminal fear.[11]
People were exposed to a subliminal image flashed for 16.7
milliseconds that could signal a potential threat and again with a
supraliminal image flashed for half a second. Furthermore,
supraliminal fear showed more sustained cortical activity, suggesting
that subliminal fear may not entail conscious surveillance while
supraliminal fear entails higher-order processing.[11]
Emotion eliciting stimuli[edit]
A subliminal sexual stimulus has a different effect on men compared to
women.[16] Men and women were subliminally exposed to either a sexual
or a neutral picture, and their sexual arousal was recorded.
Researchers examined the accessibility of sex-related thoughts after
following the same procedure with either a pictorial judgment task or
lexical decision task. The results revealed that the subliminal sexual
stimuli did not have an effect on men, but for women, lower levels of
sexual arousal were reported.[16] However, in conditions related to
accessibility of sex-related thoughts, the subliminal sexual stimuli
led to higher accessibility for both men and women.[16]
Subliminal stimuli can elicit significant emotional changes, but these
changes are not valuable for a therapeutic effect.[17] Spider-fearful
and non-fearful undergraduates experienced either a positive,
negative, or neutral subliminal prime followed immediately by a
picture of a spider or a snake. Using visual analogue scales, the
participants rated the affective quality of the picture. No evidence
was found to support that the unpleasantness of the pictures can be
modulated by subliminal priming.[17] In fact, the non-fearful
participants rated the spiders as more frightening after being primed
with a negative stimuli, however, for the fearful participants, this
effect was not found.[17]
Simple geometric stimuli[edit]
Laboratory research on unconscious perception often employs simple
stimuli (e.g., geometric shapes or colors) in which visibility is
controlled by visual masking.[18] Masked stimuli are then used to
prime the processing of subsequently presented target stimuli. For
instance, in the
Response PrimingResponse Priming paradigm, participants have to
respond to a target stimulus (e.g., by identifying whether it is a
diamond or a square) which is immediately preceded by a masked priming
stimulus (also a diamond or a square). The prime has large effects on
responses to the target; it speeds responses when it is consistent
with the target, and slows responses when it is inconsistent. Response
priming effects can be dissociated from visual awareness of the prime,
such as when prime identification performance is at chance, or when
priming effects increase despite decreases in prime visibility.[18]
The presentation of geometric figures as subliminal stimuli can result
in below threshold discriminations.[19] The geometric figures were
presented on slides of a tachistoscope followed by a supraliminal
shock for a given slide every time it appeared. The shock was
administered after a five-second interval. Electrical skin changes of
the participants that occurred before the reinforcement (shock) or
non-reinforcement were recorded. The findings indicate that the
proportion of electrical skin changes that occurred following
subliminal visual stimuli was significantly greater than expected.[19]
In contrast, the proportion of electrical skin changes that occurred
in response to the stimuli which were not reinforced was significantly
less. As a whole, participants were able to make below threshold
discriminations.[19]
Word and non-word stimuli[edit]
Another form of visual stimuli are words and non-words. In a set of
experiments, words and non-word were used as subliminal primes. Primes
that work best as subliminal stimuli are words that have been
classified several times before they are used as primes. Word primes
can also be made from parts of practiced words to create new words. In
this case, the actual word used as a prime can have the opposite
meaning of the words it came from (its “parents”), but it will
still prime for the meaning of the parent words. Non-words created
from previously practiced stimuli have a similar effect, even when
they are unpronounceable (e.g., made of all consonants). These primes
generally only increase response times for later stimuli for a very
short period of time (milliseconds).[22]
Masking visual stimuli[edit]
Visual stimuli are often masked by forward and backward masks so that
they can be displayed for longer periods of time, but without the
subject being able to tell what the prime is. A forward mask displayed
before the prime for a short period of time and usually a backward
mask will follow the prime. This prevents recognition of the prime by
the subject.[23]
Auditory stimuli[edit]
Auditory masking[edit]
One method for creating subliminal auditory stimuli is called masking.
This method involves hiding the target auditory stimulus in some way.
Auditory subliminal stimuli are shown to have some effect on the
participant, but not a large one.[23] For example, one study used
other speechlike sounds to cover up the target words.[23] The study
found evidence of priming in the absence of awareness of the stimuli.
But the effects of these subliminal stimuli were only seen in one of
the outcome measures of priming, while the effects of conscious
stimuli were seen in multiple outcome measures.[23] However, the
empirical evidence for the assumption of an impact of auditory
subliminal stimuli on human behavior remains weak: In an experimental
study on the influence of subliminal target words (embedded into a
music track) on choice behavior for a drink,[24] authors found no
evidence for a manipulative effect.
Self-help audio recordings[edit]
A study investigated the effects on self-concept of Rational Emotive
Behavior Therapy and auditory subliminal stimulation (separately and
in combination) on 141 undergraduate students with self-concept
problems. They were randomly assigned to one of four groups receiving
either Rational-Emotive Therapy, subliminal stimulation, both, or a
placebo treatment. Rational-Emotive Therapy significantly improved
scores on all the dependent measures (cognition, self-concept,
self-esteem, anxiety), except for behavior. Results for the subliminal
stimulation group were similar to those of the placebo treatment
except for a significant self-concept improvement and a decline in
self-concept related irrational cognitions. The combined treatment
yielded results similar to those of Rational-Emotive Therapy, with
tentative indications of continued improvement in irrational
cognitions and self-concept from posttest to follow-up.[25]
Another study investigated the effects of self-help tapes on
self-esteem and memory. Volunteers who wanted to improve their
self-esteem or memory were recruited and completed several self-esteem
and memory tests before being given a self-help tape. Subjects were
given a self-esteem audio tape or a memory audio tape, but half of the
tapes were mislabeled and half were correctly labeled. After listening
to the tapes daily for five weeks, subjects came back and repeated the
self-esteem and memory tests. There was no significant change from the
first set of testing to the second, although subjects believed that
their self-esteem or memory improved based on which tape they believed
they had, even when they had a mislabeled tape (those who had tapes
labeled as self-esteem tapes felt their self-esteem had increased and
the same with memory). This effect is often referred to as a
placebo.[26][27] There are multiple other studies on subliminal
self-help with different measures and have given similar
results.[28][29]
Consumption and television[edit]
Some studies have looked at the efficacy of subliminal messaging in
television. Subliminal messages produce only one-tenth of the effects
of detected messages and the findings related the effects of
subliminal messaging were relatively ambiguous.[30] Also,
participants’ ratings of positive response to commercials are not
affected by subliminal messages in the commercials.[30]
Karremans suggests that subliminal messages have an effect when the
messages are goal-relevant.[31] Subliminally priming a brand name of a
soft drink (Lipton Ice) made those who were thirsty want the Lipton
Ice. However, those who were not thirsty were not influenced by the
subliminal messages.[31] Karremans did a study assessing whether
subliminal priming of a brand name of a drink would affect a person's
choice of drink, and whether this effect is caused by the individual's
feelings of being thirsty.[31] In another study, participant's ratings
of thirst were higher after viewing an episode of
The SimpsonsThe Simpsons that
contained single frames of the word "thirsty" or of a picture of a
Coca-Cola can.[32] Some studies have shown greater effects of
subliminal messaging with as high as 80% of participants showing a
preference for a particular rum when subliminally primed by the name
placed in an ad backward.[33]
Many authors have continued to argue for the effectiveness of
subliminal cues in changing consumption behavior, citing environmental
cues as a main culprit of behavior change.[34] Authors who support
this line of reasoning cite findings such as the research that showed
slow-paced music in a supermarket was associated with more sales and
customers moving at a slower pace.[35] Findings such as these support
the notion that external cues can affect behavior, although the
stimulus may not fit into a strict definition of subliminal stimuli
because although the music may not be attended to or consciously
affecting the customers, they are certainly able to perceive it.
Subliminal messaging is prohibited in advertising in the United
Kingdom.[36]
See also[edit]